CHICAGO (AP) — A storm with a 2,000-mile footprint threatened to frustrate Christmas travelers from Texas to Nova Scotia with a little of everything Mother Nature has to offer, from freezing rain, ice and snow to flooding, thunderstorms and possibly some tornadoes in the South.

Some of the millions of people hitting the roads and airports Saturday squeaked through before any major weather hit, but as the afternoon wore on some cancellations and delays started to mount at major aviation hubs. Forecasters said roads that are passable one minute could become treacherous the next as a cold blast on the backend of the storm turns rain to ice and snow.

Making it harder for forecasters to stay a step ahead, the system was a weird swirl of wintry and spring-like weather as it passed over areas in the Midwest with freezing temperatures and places like Nashville, where it could surpass 70 degrees.

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“This is a particularly strong storm with very warm, near record-breaking temperatures in the East and very cold air in the Midwest, and that contrast is the sort of conditions that are favorable for not only winter weather but also tornadoes,” said National Weather Service meteorologist Ed Danaher in College Park, Md.

The worst of the storm was expected to hit Midwest population centers on Saturday evening, giving some travelers a window at the start of the holiday rush to get through airports and along highways with little disruption. Flight cancellations were creeping up above 400 around the country, according to aviation tracking website FlightAware.com. Most of the disruptions were affecting flights in and out of major hubs like O’Hare International Airport in Chicago, though the weather there was not yet nasty.

Other major airports being affected Saturday afternoon included Dallas/Fort Worth International and Denver International.

It’s bad timing for the estimated 94.5 million Americans planning to travel by road or air during this holiday season, which runs from Saturday through New Year’s Day, and those hitting the roads for some last-minute shopping.

The storm had several bands of strikingly different weather.

In the Upper Midwest, forecasters expected 6-8 inches of snow north and west of Chicago and into Wisconsin.

It was already bringing significant ice accumulations to Oklahoma, southern Missouri and northern Arkansas, splitting trees and snapping power lines. That was expected to change over to snow by Saturday night.

Parts of Maine could get more than a half-inch coating of ice, which would make roads treacherous and cause widespread power outages.

“The best advice for everyone is just to really pay attention. With every few hours, we’re going to get better information,” Maine Emergency Management Agency spokeswoman Lynnette Miller said Friday.

The weather service issued a flash flood watch from Arkansas northeastward through parts of Missouri, Illinois, Indiana and Ohio, with up to 4 inches of rain projected. With falling temperatures, some of that could be freezing rain by Saturday night in the St. Louis area, weather service meteorologist Jon Carney said.

In Indiana, the National Weather Service posted flood warnings along southern and central Indiana streams and predicted the highest flood crests along the East Fork of the White River since April 2011.

While the Midwest and Plains were preparing for ice and snow, residents down South were concerned about tornadoes, which forecasters said were possible this weekend even though they are uncommon this time of year. The area most threatened stretched from central and northeastern Texas through Louisiana, Mississippi, Arkansas and southeast Missouri, where 80 mph wind gusts and flash flooding were possible.

Rain and ice in Oklahoma were blamed for two fatal traffic accidents and thousands of power outages. A 16-year-old boy died early Saturday after his car crashed and overturned on U.S. 64 near Tulsa, according to the Oklahoma Highway Patrol. And Oklahoma City police said a woman was killed Friday night in a collision on a slick roadway.

Forecasters said up to a half-inch of ice could accumulate across the middle of the state.

A woman sleeping in a hotel in Holland in western Michigan was injured when a motorist lost control of his car on an icy street early Friday and slammed into the wall outside her room, MLive.com reported.

The weather wasn’t the only headache maker. A baggage-equipment breakdown lasted for hours at Lambert-St. Louis International Airport, creating a backed-up line of travelers that stretched onto the sidewalk outside one of the terminals.

If there is a silver lining, it’s that Christmas happens mid-week this year, AAA spokeswoman Heather Hunter said.

“When a holiday falls on a Wednesday it gives travelers more flexibility of either leaving the weekend before, or traveling right before the holiday and extending the trip through the following weekend,” Hunter said.